Activation and deactivation of Pt containing sulfated zirconia and sulfated zirconia studied by in situ IR spectroscopy

In situ infrared spectroscopy (IR), thermogravimetric measurements (TG) and temperature-programmed evolution of gases (TPE) have been used to study activation and regeneration of sulfated zirconia with and without Pt (SZ, Pt/SZ). Isomerization and cracking of n-heptane was used as test reaction. The first activation of Pt/SZ is independent of the atmosphere, air or He and N-2, in each case the catalyst was active. But it was necessary to regenerate the catalyst in air to obtain the initial activity and selectivity. When regeneration was done in helium or nitrogen the catalyst lost its acid properties and only hydrogenolysis of n-heptane to propane and n-butane was observed. This can be explained by a loss of a part of sulfates between 400 and 500 degreesC measured by TG and TPE. In the IR spectrum the intensity of the SO band at 1400 cm(-1) decreased and shifted to lower wavenumbers whereas the band of terminal Zr-OH groups at 3740 cm(-1), which was absent in the first spectrum after activation increased. The activation conditions of SZ are independent of the atmosphere, no loss of sulfate groups was observed. The reason for deactivation of SZ is coke formation during alkane conversion.